Electric lamp having an outer bulb

ABSTRACT

The lamp comprises a discharge vessel ( 2 ), which is sealed in a vacuum-tight manner and is arranged in an outer bulb ( 12 ) which only partially surrounds the discharge vessel. The outer bulb comprises an open tube, which is closed by sheet-metal parts.

TECHNICAL FIELD

The invention relates to an electric lamp having an outer bulb and having an inner vessel, in particular a discharge vessel, arranged therein, the inner vessel being elongate and having two ends, the ends having seals, and the outer bulb only partially surrounding the inner vessel. Of concern here are, in particular, discharge lamps such as metal halide lamps, or else halogen incandescent lamps.

BACKGROUND ART

U.S. Pat. No. 2,004,0253897 has disclosed an electric lamp having an outer bulb, in the case of which the outer bulb only partially surrounds the inner vessel made from glass. The outer bulb is itself produced from glass and is fixed to the seals of the inner vessel. This partially covering outer bulb could in this case be fixed using an established technique by means of glass shaping and subsequent glass-to-glass fusing. However, it has been shown that these steps overall have relatively stringent requirements in terms of machine capacity and energy.

DISCLOSURE OF THE INVENTION

One object of the present invention is to provide an electric lamp having an outer bulb and having an inner vessel, in particular a discharge vessel, arranged therein, the inner vessel being elongate and having two ends, the ends having seals, and the outer bulb only partially surrounding the inner vessel, which lamp makes simple and cost-effective production possible.

This object is achieved by the following features:

the outer bulb is an open tube made from glass and having two ends, at least one end being sealed by an essentially planar sheet-metal part made from resilient sheet metal, the sheet-metal part being fixed on the associated seal.

Particularly advantageous refinements are described in the dependent claims.

The electric lamp according to the invention has an outer bulb and an inner vessel, usually a discharge vessel, which is arranged therein and is sealed in a vacuum-tight manner. However, the electric lamp according to the invention may also be a halogen incandescent lamp having an outer bulb.

The novel connection between the inner vessel and the outer bulb makes possible a purely mechanical mounting system, which is based on sheet-metal clips. This considerably reduces the machining complexity and also no longer requires any heating energy. The novel concept is particularly suitable in cases in which a specific atmosphere is not required in the outer bulb, for example a vacuum or a pure nitrogen atmosphere.

One particularly preferred embodiment, in which the advantages of the novel concept are particularly prevalent, is an arrangement in which the outer bulb is sealed by sheet-metal parts at both mutually opposing ends of the inner vessel. Typical applications are metal halide lamps and halogen incandescent lamps.

Of particular concern is an electric lamp having an outer bulb and having an inner vessel, in particular a discharge vessel, arranged therein, the inner vessel being elongate and having two ends, the ends acting as seals, and the outer bulb being an open tube made from glass and having two ends, at least one end being sealed by an essentially planar sheet-metal part made from resilient sheet metal, the sheet-metal part being fixed on the associated seal. The inner vessel can in this case either be made from glass, usually quartz glass or hard glass, or from ceramic.

The sheet-metal part is preferably of annular design, the outer diameter of the ring approximately corresponding to the outer diameter of the open tube.

In order to hold the sheet-metal part on the tube, lugs, which are bent back through approximately 90° and bear on the inside against the tube in a clamping manner, are preferably distributed over the circumference of the outer diameter of the sheet-metal part. Another way of holding the sheet-metal part on the tube is a circumferential bent-back cover rim, which is fixed to the tube, for example, by means of an adhesive compound.

The outer bulb is centralized in a simple manner when the seal has a circular cross section in the form of a cylinder.

In particular, the sheet-metal part has a central opening which is matched to the cross section of the seal. The seal is usually in the form of a fuse seal having a circular-cylindrical cross section. The seal may, however, also be a pinch seal, whose cross section is essentially rectangular.

A particularly simple way of stopping and holding the sheet-metal part securely on the seal is achieved by the seal being cylindrical with a given diameter and opening out over one edge into an extension part which is in the form of an open tube having a relatively large diameter, the diameter of the central opening of the sheet-metal part being matched to that of the seal.

The outer bulb is fixed in a clamping manner by the lugs of the sheet-metal part not being straight but being bent out in the manner of a roof.

The sheet-metal part is matched to the seal by a zone, which surrounds the central opening, of the sheet-metal part being bent out slightly from the plane of the sheet-metal part.

This is preferably achieved by the zone being divided into a plurality of tabs by means of radial slots, said tabs being capable of individually being bent up slightly.

The two seals are preferably designed such that the tube can be open on both sides and can be sealed at both ends by identical sheet-metal parts. However, it is not impossible for one end of the tube to be fixed to the seal in a conventional manner as in the prior art.

In the case in which a specific atmosphere is desired in the outer bulb, the outer bulb can be kept air-tight or vacuum-tight by a suitable sealing means, such as a sealing ring, being introduced in the contact region between the sheet-metal part and the end of the open tube.

In one preferred embodiment, the inner vessel is sealed at two mutually opposing ends with identical seals, the outer bulb being fixed to identical seals of the inner vessel at both ends by means of a sheet-metal part.

At least some of the sheet-metal part can, in particular, be coated by an oxidic layer, in particular titanium oxide, in order to prevent photo ionization being produced by means of UV radiation. Furthermore, the oxidic layer improves thermal insulation.

A method for producing a lamp having an outer bulb follows the following steps, namely that an open tube is pushed centrally over an inner vessel, and then a sheet-metal part is placed onto the open end of the tube, the lugs being bent back through approximately 90°, and the central opening being selected to be slightly smaller than the cross section of the associated seal, with the result that, when it is placed on the seal, the central opening is enlarged to the diameter of the seal by the individual tabs of the surrounding zone being bent out slightly from the plane of the sheet-metal part.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below with reference to a plurality of exemplary embodiments. In the drawings:

FIG. 1 shows a perspective side view of a metal halide lamp;

FIG. 2 shows various views of one exemplary embodiment of a sheet-metal part;

FIGS. 3 to 5 show various views of further exemplary embodiments of a sheet-metal part; and

FIG. 6 shows a side view of a further exemplary embodiment of a halogen incandescent lamp.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows the perspective view of a metal halide lamp 1 sealed at two ends. The discharge vessel 2 which is in the form of a barrel body and is made from quartz glass (or else Al₂O₃ ceramic) encloses two electrodes 3 (only one is visible) in addition to a metal halide filling. A coating 11 is applied at the level of the electrodes 3. The bulb ends are sealed off by means of fuse seals 4, in which foils 5 are embedded. These foils 5 are connected to outer power supply lines 6. The outer power supply line 6 is guided in a tubular sleeve 7 and ends at a base part (not illustrated). The central part of the discharge vessel is surrounded by an outer bulb 12.

The outer bulb 12 comprises a tube 13 which is open at both ends, is made, for example, from hard glass and has a considerably larger diameter than the discharge vessel 2. A sheet-metal part 14 in the form of a disk-shaped circular ring is fixed to each of the ends of said tube 13. The outer diameter of the sheet-metal part 14 approximately corresponds to the diameter of the open tube 13. Bent-back lugs 15, which guide the tube 13, are distributed over the circumference.

The sheet-metal part 14 also has a central opening 19, as shown in FIG. 2, which is matched to the cross section of the associated seal 4.

In order to reliably achieve this aim, a zone 20, which is bent out slightly from the plane of the sheet-metal part, adjoins the central opening. For this purpose, the zone 20 is divided into five tabs 21, which are separated from one another by radially extending slots 22.

In the still uninstalled state, these tabs 21 are initially almost in the same plane as the rest of the sheet-metal part, but, in contrast, are bent back through approximately 5°. If the sheet-metal part 14 is pushed onto the sleeve 7, the tabs open out and in the process increase the size of the central opening, in which case they surround it closely. The diameter of the seal 4 is slightly smaller than that of the sleeve 7, with the result that the tabs are anchored on the edge 23 there between if they slide over the sleeve 7 finally onto the seal 4.

In the still uninstalled state, the lugs 15 are likewise initially in the plane of the sheet-metal part 14, since initially they are stamped out, cf. FIG. 2 a. The stamped sheet-metal part is only then preprocessed by the lugs being bent back through approximately 90° and the base of the zone being perforated, if appropriate. Only then is the sheet-metal part pushed onto the seal. See in this regard the schematic sectional illustration shown in FIG. 2 b and the perspective illustration shown in FIG. 2 c, in each case in the bent-back state.

FIG. 3 shows one exemplary embodiment of a sheet-metal part 25 having a continuously circumferential rim 26 made from spring steel. This rim 26 can be fixed to the open end of the tube 13 by means of adhesive, as a result of which an air-tight seal is made possible there. However, it is generally sufficient if the two sheet-metal parts merely fix the outer bulb between them, in which case they themselves are stopped at the edge of the seal. Another possibility for the outer bulb being kept air-tight is for a sealing ring 40 to be introduced in the contact region between the sheet-metal part and the end of the open tube 13, cf. FIG. 3 b.

FIG. 4 shows a sheet-metal part 27 having a rectangular opening 28. This sheet-metal part 27 is especially suitable for discharge vessels having a pinch seal as the seal.

FIG. 5 shows an exemplary embodiment of a sheet-metal part 30 having lugs 31, which are bent back out slightly in the form of a roof. This embodiment also fixes the outer bulb 13 in a clamping manner such that rattling noises are reliably suppressed.

Finally, FIG. 6 shows a halogen incandescent lamp 35, in the case of which one end 36 of the outer bulb is fixed in a manner known per se to the seal 4 of the inner vessel by means of being integrally formed on a bead 37. The other open end 38 of the outer bulb is fixed to a sheet-metal part 14, as described.

In this case, the central part 12 of the outer bulb has a larger diameter than the ends 36 and 38. The open tube 7 behind the fuse seal 4 has a markedly larger diameter than said fuse seal 4, as a result of which the sheet-metal part 14 is stopped reliably at the edge there between. Although such an edge is not absolutely necessary if the spring force of the sheet-metal part is selected to be sufficiently high, it does considerably improve the stopping effect. 

1. An electric lamp having an outer bulb and having an inner vessel, in particular a discharge vessel, arranged therein, the inner vessel being elongate and having two ends, the ends having seals, and the outer bulb only partially surrounding the inner vessel, wherein the outer bulb is an open tube made from glass and having two ends, at least one end being sealed by an essentially planar sheet-metal part made from resilient sheet metal, the sheet-metal part being fixed on the associated seal.
 2. The lamp as claimed in claim 1, wherein the sheet-metal part is in the form of a disk, the outer diameter of the disk approximately corresponding to the outer diameter of the end of the open tube.
 3. The lamp as claimed in claim 2, wherein lugs, which bear on the inside against the end of the tube are distributed over the circumference of the outer diameter of the sheet-metal part.
 4. The lamp as claimed in claim 2, wherein the sheet-metal part has a central opening which is matched to the cross section of the seal.
 5. The lamp as claimed in claim 4, wherein the sheet-metal part is held securely on the seal by the seal being cylindrical with a given diameter and opening out over one edge into an extension part which is in the form of an open tube having a relatively large diameter, the diameter of the central opening of the sheet-metal part being matched to that of the seal.
 6. The lamp as claimed in claim 5, wherein the zone is divided into a plurality of tabs by means of radially extending slots.
 7. The lamp as claimed in claim 3, wherein a clamping action of the sheet-metal part on the tube is achieved by the lugs being bent out in the manner of a roof.
 8. The lamp as claimed in claim 1, wherein the seal has a circular cross section and, in particular, represents a fuse seal.
 9. The lamp as claimed in claim 1, wherein the outer bulb is kept air-tight by a sealing ring being introduced in the contact region between the sheet-metal part and the end of the open tube.
 10. The lamp as claimed in claim 1, wherein the inner vessel is sealed at two mutually opposing ends by means of identical seals, the outer bulb being fixed to the seals of the inner vessel by means of two sheet-metal parts.
 11. A method for producing a lamp having an outer bulb as claimed in claim 1, wherein an open tube is pushed centrally over an inner vessel, and then a sheet-metal part is placed onto the open end of the tube, the lugs being bent back through approximately 90°, and the central opening being selected to be slightly smaller than the cross section of the associated seal, with the result that, when it is placed on the seal, the central opening is enlarged to the diameter of the seal by the individual tabs of the surrounding zone being bent out slightly from the plane of the sheet-metal part. 